Reorganization of microtubular cytoskeleton and formation of cellular processes during post-telophase in Haemanthus endosperm

We followed time-dependent post-telophase reorganization of the microtubule cytoskeleton on immunostained preparations of endosperm of the higher plan t Haemanthus. After completion of mitosis, the phragmoplast continued to re organize for several hours. This prompted the formation of phragmoplast-lik e derivatives (secondary and accessory phragmoplasts and peripheral microtu bular ring). Next, elongated cellular protrusions (processes) appeared at t he cell periphery. These processes contained long microtubule bundles and d isorderly arranged actin filaments. Microtubule converging centers or acces sory phragmoplasts were often present at the tips of the processes. Observa tion in vivo demonstrated that processes were formed at the cell periphery as extensions of lammelipodia or filopodia-type protrusions that commonly t erminated with cytoplasmic blobs. We suggest that processes are derivatives of a peripheral microtubular ring that reorganizes gradually into cellular protrusions. Endosperm processes have several features of neuronal cells, or animal somatic cells with overexpressed MAPs. Since microtubule-containi ng processes were never detected shortly after extrusion of the cells from the embryo sac, this course of events might be restricted specifically to e xtruded endosperm and triggered either by removal of cells, their placement in monolayer on agar substrate, or both. Thus, post telophase behavior of endosperm cells offers a novel experimental system for studies of cytoskele ton in higher plants. (C) 1999 Wiley-liss, Inc.